Who is running a aftermarket rear that is quiet?

[Boostable]

My Moser is pretty quite!! But then again Im still pushing the car around

In all seriousness, I hope there is not an issue as with some of you other guys I have had mine awhile, and will be more then a year before she see's the road from time of purchase.

[cluxford]

Strange locker in mine
35 spline
355 gears

can't hear anything over the roar of the 632 cube BBC running through twin 3" pipes and single magnaflows

[4mul8ion]

Originally Posted by Sieg

I've been intrigued with acoustical damping ever since watching a show featuring an Aston Martin assembly facility on Velocity TV where an "engineer" was strategically applying a material similar to Dynamat Extreme in lightening bolt and wave shapes on interior cabin panels. I've always wondered how much science was behind their application considering the sophistication of their engineering.

I finally found a picture (and a great tour of the facility) tonight.





http://www.speedhunters.com/2013/08/...dream-factory/

Very cool.

There's probably quite a bit of science behind those shapes. Check out this video that shows a flat plate going into motion at various frequencies.

[4mul8ion]

Originally Posted by Twoblackmarks...

...
Here we have a lot of modified cars like Voyager type cars With removed rear seat and changed carpets and different stuff, (because of TAXES!) Many of those complain about noises from everything, since the rear compartment now acts as a huge speaker.
...

That's a great point. I'll be running 3.55s from us gear and I don't remember what was put down for lining my trunk.

[Sieg]

If my post was cool........your's ranks as Ubercool!

It would be interesting to apply sections of Dynamat to the underside of the test sheet to see how it impacts the patterns.

Flat plate in set gauges is one thing, plate formed by stamping has to be an entirely different animal.

Are there sensors that can be applied to plate to measure frequencies?

Thanks for the education!

[4mul8ion]

Thanks. This has been a fun discussion but apologies to 69x22 for pulling the topic of this post not just into the weeds but now through the weeds, through the guard rail and halfway into the corn field.

You're absolutely right. Formed steel is completely different. With different boundary constraints, bends and dimples, you can change the performance of the panel. They test it by having something apply a known force and measure the response using an array of accelerometers to measure the response.



Dynamat has done something to determine the effects of their acoustic material to the patterns. Look at what they say for their XTreme product.
http://www.dynamat.com/technical_spe...at_xtreme.html

I'm not sure what the effective absorbing range it can cover but for gear noise it needs to be most effective in the 300 - 600 Hz range to absorb gear mesh frequencies. That product may only be effective at absorbing lower road noise related frequencies.

Not sure on that.

[4mul8ion]

Originally Posted by Blake Foster

We have sold a lot of rearends. Strange and Currie, and Rons Rear ends, we have seen issues with Strange and Currie none with Rons, the biggest issue we have seen is with 3:73 gears.
Currie suggests 80-140 GL5 gear oil
Here is the deal, My Nova, My Camaro, both have run synthetic since day 1, neither got the "Proper break in" and NEITHER make a sound. I know that only confuses the issue.
We did one and it sounded like you were dragging a cat behind you, yes the MFG said send it back, and yes they changes the gears to 3:89's (from 3:73)but I too am with everyone else, why should the Customer(or shop) have to cover all the costs? the second set was only a bit better. now what???
HOW is it that the OEM's can do THOUSANDS of gears a DAY and not have one that makes noise, and the aftermarket we are just to put up with it.???Oh yea you have the option of spending another 300 to have them micro polished still there is no Guarantee they will not be quiet....... Why NOT?
Riddle me that?

The micro polishing process is just a tooth surface finish refinement only. It is supposed to polish out the cutter marks left over from manufacturing the gear. Classic gear noise comes from errors in the tooth profile as the teeth mesh together. If there is a tooth surface finish problem it will generally sound like a jet engine in the back. Very high frequency.

To make a gear, you have to turn the forgings, cut the teeth on the pinion, cut the teeth on the ring gear, heat treat quench and temper both, hard finish the bearing on the pinion and finish the bore and backface on the ring gear. Then hard finish the teeth by either lapping a pinion and gear together or grinding the tooth profile of each member.

As the cutter wears, the tooth profile changes and the cutter no longer cuts the part but starts to tear material off leaving a scratchy tooth surface. You can compensate for this cutter wear by adjusting the machine but if the cutter is too worn out, you're out of adjustment, the tooth geometry becomes less than ideal, the ridges are too deep and the hard finishing process isn't as effective.

Check out the video library of Precision gear explaining the gear cutting process in Chapter 4. Warning: terrible sound.
http://www.precisiongear.com/pgmanvideo.htm